It is impossible to say with the information you have given. There's more than a factor of 10 difference in performance between the slowest i7 processors and the fastest i7 processors. Knowing exactly the specific models you're comparing is vital here.
The question of "RAM-efficiency" really hasn't got much to do with the CPU itself. As the i7 CPUs and the Apple Silicon CPUs are all 64-bit processors, there's not much about the CPU that determines "RAM-efficiency" - that is almost entirely down to the operating system and your applications.
There are minor advantages to modern CPUs in terms of having a performance surplus that allows you to enable better memory compression than you would on a really old system - and there are some benefits of having multiple page sizes, etc. However, that usually does not make any practical difference when comparing a fairly recent i7 to the Apple Silicon CPUs.
UPDATE
You have now specified that you're comparing with an i7-5557U processor. That's a CPU from 2015. In terms of generic benchmarking, you would expect even the slowest M1 CPU to be 4-5 times faster than your old CPU. However, remember that's benchmarking and doesn't apply 1:1 to your actual work-flow. Especially make note that there's a big difference between single-threaded performance and multi-threaded performance on modern CPUs.
Also note that this type of benchmarking only relates to the compute-performance of the CPU - not to the entire system that makes up the computer. The difference in RAM size (8 GB vs 16 GB) can make a huge difference for your particular work-flow. I.e. if you mainly use your computer for things that take up 16 GB of RAM, but really does not use the CPU - then that is probably going to run less smooth on an 8 GB system.
To sum it up, noting that it is highly subjective and really dependent on your particular work-flow, then in general most users would expect and find that a new M1 system performs vastly better than an i7 2015 MacBook Pro.